Method of producing ceramic molds for diamond tools



July 19, 1949. w. G. LAKE 2,476421 METHOD OF PRODUCING CERAMIC MOLDS FOR DIAMOND TOOLS Filed Sept. 5, 1945 PatentedJuly 19, 1949 METHOD OF PRODUCING CERAMIC MOLDS FOR DIAMOND TOOLS William G., Lake, Toronto, Ontario, Canada, as-

signor to J. K. Smit & Sons, Inc., New York, N. Y., a corporation of New York Application September 15, 1945, Serial No. 616.631

In Canada May 3, 1945 This invention relates to the manufacture of powdered metal articles and more specifically to the manufacture of metal powder, diamond-bearing cutting tools such as drilling bits and the like and the molds therefor.

In the manufacture of rock drilling 'bits and analogous articles 'in which the cutting section is obtained by protruding diamonds, it has been the practice to utilize a carbon mold with small depressions in the face of the mold cavity, the diamonds being spotted in these depressions. After this the mold is filled with metal powder and the metal 'is rendered solid by the application of heat and pressure.

The use of carbon molds, however, in the manufacture of metal powder diamond' tools is not entirely satisfactory for several reasons. The cost of a'suitable grade of canbon for molds in the powder metallurgy process is very high, and I the machining o perations 'required to :producemolds from carbon raw material in quantity also has had a retarding influence upon the production of diamond tools by this method; the necessity for laying out or plotting the diamond pattern in drill bit molds is also a costly item and does not lend itself to quantity production; this is particularly true in the case of diamond drill hits where the practice is for the diamond content to be sold on the number of Stones and carat weight basis, and it is practically impossible to adhere to such practice by free hand or individual laying out of carbon molds. Owing to the high cost of carbon molds it is very desrable that more than one bit or tool be obtained from each mold. However this is difiicult because of breakage of the mold when removing the tool, and as each successive tool is withdrawn the mold becomes worn and the tools become progressively larger, adversely affecting adherence to specifications.

Furthermore, the use of carbon for molds for sintering renders the control of the furnace atmosphere diflicult, if not impossible, so that the carbon content of steel parts, used as inclusions with parts being manuf actu-red, is unpredictable. Then again the behavior of carbon at eleva-ted temperatures makes it necessary to compensate for expansion and contraction of the mold by making the mold of difierent dimensions than those required in the finished articles.

One of the objects of my invention is to overcome the o bjections above noted in connection with conventional methods of making diamond bits and other diamond tools. To attain this object I make use of ceramic molds. The cost of such molds is negligble, in that an average size 1 Claim. (Cl. 25-156) but a few cents. Under my method a master pattern can be made from a machinable free material from which any quantity of ceramic molds can be made. It will be appreciated also that identical parts can be produced in quantity, due

to the fact that any number of ceramic molds' can be made identical from one master pattern. Inasmuch as ceramic molds 'can be produced at such low cost it becomes feasible to use a new mold for each tool, so that adherence to size is maintained.

No trouble is experienced with furnace atmosphere when employing ceramic molds, in that such molds are composed of *inert materials and in their manufacture are subjected to temperatures in excess of those employed in sintering the metal powders of the tool being manufactured; it will be appreciated also that for the same reason no expansion or contraction occurs in the sintering operation, therefore no compensation for such is necessary. It will, therefore, be appreciated that the size of a part made in the ceramic mold is predetermined 'by mold size and is identical to this dimension.

In diamond tools, such as diamond bits and the like, it is essential that the diamonds be accurately locatedover the ace of the tool and, furthenmore, it is essential that the protrusion of the diamonds from the completed article be very accurately controlled. It is, therefore, a further object of the present invention to provide a mold in which the diamonds are accurately located both with respect to the outer surface of the bit and to each other.

As above mentioned. it is possible to manufacture molds of ceralmic material which are sufficiently refractory to withstand the heat of sintering of the metal powders and which are strong enough to withstand the stresses caused by the pressure during hot and cold pressing of the powdered material. These molds can be manufactured by a molding operation entailing the use of dies. However, because of the multiplicity of diamond :patterns normally employed, and the hardness of the ceramic in its completed form, it has been necessary to devise a means for molding a ceramic material which does not require the use of expensive metal dies which require many machining Operations.

It is, therefore, a further object of the present invention to provide a method for molding ceramic 'articles which does not require expensive machine Operations upon die material.

Referring now to the drawings:

Fig. 1 is a perspective view of a typical dia- 3 mond-bearing cutting tool made according to the process about to be described:

Fig. 2 is a section of the ceramic mold used in manufacturing the diamond-hearing tool shown' in Fig. 1:

Fig. 3 is a fragmentary section of a device used ;for producing the mold of Fig. 2;

Fig. 4 is a detail oi a part of the device shown in Fig. 3; and

Fig. 5 is a mold used in producing the device shown in Fig. 4.

Briefiy the diamond-hearing tool shown in Fig. 1 consists of a steel shank 2 threaded for attachment to a drilling stem. In this form of bit. cutting and abrading are accomplished by a number ot' diamonds 4 which project siightiy from the face of the annular surfaces of the bit. These diamonds are held in a matrix 6 which is produced by compressing and heating a suitable metallic powder.

The prior methods of manufactureof tools of this type involve the use of a carbon mold having a cavity therein of such form as properly to shape the tool head. In the wails of this cavity the diamond pattern is carefuliy laid out and small depressions formed therein to receive the diamonds before the powdered metal is poured into the mold. such a mold is substantially of the form shown in Fig. 5.

In the method contemplated by the present invention ceramic molds of the type shown in Fig. 2 are used for the manufacture of these tools. These molds are to be formed in dies, part of which are in turn formed in the molds of a type shown in Fig. 5 of easily machinable material such .as carbon'. As can be seen, the mold of Fig. 5 consists of a generaily cylindrical carbon block 8 having a cavity o formed therein which is of the same general shape as the completed cutting head. The inner surfaces of the cavity o have' Smail depressions |2 formed therein which correspond to the positions of the diamonds to be present in the completed. bit, while grooves N on the annular surfaces of the cavity serve to locate the gauge stones. If core bits such as shown in Fig. 1 are being manufactured, then a core print is inserted in the mold. When plain i'aced bits are being manufactured, it becomes unnecessary, of course. to use a core print'.

By means of the mold shown in Fig. 5 the object shown in Fig. 4. which might be termed the pattern for the ceramic mold, is produced. This pattern is formed in a manner known in the prior art, by filling the cavity of the mold of Fig. 5 with metal powder, placing the shani: !B at the top thereof and subjecting the assembly to heat and pressure to soiidify the metal powder. The depressions |2 and grooves M in the mold of Fig. 5 produce corresponding projections Ni on the pattern head s, the reproduction being identical.

After completion of the metal powder pattern of Fig. 4 the pattern is assembled in the die device shown in Fig. 3. As can be seen, this consists essentially of a cylindrical die 20 with a pair oi' plungers 22 and 24. The piunger 22 is intended merely for the purpose of ejecting the completed mold from the cylinder 20. In practice a quantity of ceramic material, in a plastic condition. is inserted in the cylindrical die 20 and the ram or plunger 24 brought down to mold the ceramic to the desired shape, as determined by the pattern of Fig. 4. It will be seen that a conical portion 2! is provided on the pattern head ll to produce a i'unnel in the completed ceramic mold. The mold position in the mold but also fills the ceramic insuch a manner that there is less tendency for the completed tool to stick to the mold. In the case ot, coring bits, a core 32 of carbon is inserted in the depression in the ceramic mold provided by the,

portion 25 of the pattern, as shown at 32 in Fig. 2.

It then remains necessary merely to pour sufficient metal powder into the ceramic mold and place a shani: thei-cover in contact with the metal powder and subject the entire assembly to pressure and heat to solidify the metal powder. Upon completion of this operation the completed tool may be withdrawn from the mold. Any water courses which could not be conveniently molded into the tool may then be 'cut therein by grinding, and the shank may be ground down as shown in Fig. 1 to provide clearance between the body of the shank and the wall of the hole to be drilled.

It will be seen from ,all of the foregoing that my invention provides an improved method for making metal powder diamond tools and molds therefor, wherein and whereby the objections above outined with respect to conventional methods of making diamond tools from metal powder are overcome.

It will be understood that the invention above described is best defined by the appended claim and should not be limited to the precise procedure described.

What I claim is:

The method of producing ceramic molds for the production molding of diamond tools, the cutting head of which tools consists of a matrix molded from metal powder and having diamonds protruding from the face thereof, said method comprising producing a mold of machinable material and having a cavity of the same general shape as the completed cutting head, the inner surfaces of the cavity having depressions therein corresponding to the positions of the diamonds protruding from the face of the tool matrix, charging metal powder into the said mold cavity and subjecting to heat and pressure to produce a pattern of the same general shape as the cutting head with projeotions corresponding to the positions of the diamonds protruding from the face of the tool matrix, withdrawing the said pattern,

oo molding a ceramic mold about the same and withdrawing the pattern thereby to produce the desired ceramic production mold.

- W. G. LAKE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS l Number Name Date 1,902,627 Elbogen Mar. 21, 1933 2,002.580 MacDonald May 28. 1935 &129.304 Feinbloom Sent. 6. 1938 &181.452 Ford Nov. 28. 1939 

